Because the open-loop control CNC cutting machine system has the advantages of convenient operation and low price, the open-loop control reactive stepper motor is the main method adopted in our country. Although stepper motors are widely used, they cannot be used under ordinary conditions like ordinary AC (direct) flow motors. The running speed from the starting point to the end point is under theoretical conditions. The limit starting frequency of the CNC cutting machine motor is greater than the running speed. At the speed, the motor can run as required and can reach the expected operating speed. When running to the end of the stroke, it can also immediately send out a pulse that can achieve the stop function and stop the motor. However, the actual situation of the CNC cutting machine is that the limit start rate that the stepper motor can achieve is low, which is far from meeting the requirements of higher running speed. In this working condition, if the motor is forced to start directly at the required speed (greater than the limit starting pre-set rate), "lost steps" or no response will occur. When the motor reaches the end point, although the pulse has been stopped immediately to stop it, due to the inertia effect, the phenomenon of overshooting the end point will occur, that is, overshoot will occur.
It is particularly worth noting that in order to ensure the positioning accuracy of the CNC cutting machine system (the motor's lifting speed is slow to prevent "out-of-step" or "overshoot") and to obtain a high positioning speed, mainstream systems will use the positioning process. It is divided into coarse positioning stage and fine positioning stage. According to production practice experience, "lost steps" and "overshoot" are the two most common "criminals" that seriously affect the positioning accuracy of stepper motors during operation.
The main reasons for the inaccurate positioning of CNC cutting machines include:
(1) The initial starting speed is required to be too high, exceeding the limit starting frequency of the motor, or the acceleration is too large, causing "lost steps;
(2) The power of the motor does not meet the system requirements;
(3) The working process of the actuator is subject to thousands of disturbances;
(4) The controller of the control system has malfunctioned;
(5) The pulse is lost during commutation, and the positioning in one direction is accurate, and the deviation occurs after the commutation. Although the number of commutation times increases, the deviation spring product becomes more obvious;
(6) software has design flaws;
(7) Where the timing belt is used, the software compensates too much or too little.